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<head>
    <meta charset="UTF-8">
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    <title>Document</title>
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<body>
    <input type="button"value="计算阶乘"onclick="fn01()"/>
<script>
    function  factorial(n){
        if(n==0||n==1){
            return 1;
        }
        return n*factorial(n-1);
    }
    function fn01(){
     var num=factorial(5);
     console.log(num );
    }
</script>
</body>
</html>